Particle accelerators such as linear accelerators are used today in a number of different applications such as radio therapy, radiography and sterilization. In most of these applications the particle accelerator is used to generate X rays that are applied to the object.
It is very important that a constant dose rate output from the accelerator be achieved over both the short period of time, such as during a specific therapy treatment, as well as the long period of time such as day to day during successive treatments.
One of the biggest sources of possible variation in the output from an accelerator is the change in particle output amplitude resulting from a mismatch between the operating frequency of the accelerator and the driving frequency signal applied thereto. This mismatch can result from dimensional changes in the accelerator structure due to changes in the temperature of the structure or differential expansion in different parts of the accelerator structure thereby resulting in a change in its operational frequency.
In the past, efforts to maintain desired relationship between the driving frequency source and the accelerator have been to use a stabilization device such as a stabilizing frequency cavity which is physically attached and maintained in the environment of the accelerator and stabilizes the frequency of the source to the operational frequency of the accelerator. Changes in the dimensions of the accelerator causing a change in its operational frequency would usually also be accompanied by a change in the stabilization cavity so that the stabilization cavity would stabilize the driving signal source at the desired frequency for operation of the accelerator. However, it has never been possible to perfectly match the stabilization cavity to the accelerator structure and thereby keep the driver source tuned to the best operational frequency for the accelerator.